It is known that a slide bearing made of a porous sintered metal impregnated with oil can be rotated with high precision. Since oil in the pores of the porous sintered metal is continuously supplied onto the sliding interface, frictional force can be stably kept at a low level.
The mating member with which this slide bearing is brought into contact is, in most cases, made of the same metal material as the bearing. Thus, there is neither the possibility of separation of the mating member from the bearing member, nor the possibility of these members “hugging” each other, due to a difference in linear expansion between these members. Thus by finishing this bearing with high accuracy, this bearing can be rotated with high precision.
Other self-lubricating slide bearings include one made of a resin containing tetrafluoroethylene resin (PTFE), graphite, a solid lubricant such as molybdenum disulfide, lubricating oil or wax.
If a slide bearing made of a porous sintered metal impregnated with oil is brought into sliding contact with a mating member, such as a shaft or a fixed member, that is made of a soft material, the bearing tends to abrade the mating member. If such a slide bearing runs out of lubricating oil, this could result in metal-to-metal contact.
If a slide bearing made of a resin, which has high sliding properties, is brought into a mating member made of a soft material, even though such a bearing does not attack the mating member, the bearing tends to “hug” the mating member such as the shaft when the resin expands or shrinks. In order to prevent such “hugging”, it is necessary to leave a large gap between the bearing and the mating member. But such a large gap makes it difficult to rotate the bearing with high precision.
A high-precision slide bearing which is free of this problem is proposed in the below-identified Patent document 1 which includes a radially outer portion made of a metal, and a resin layer formed on the sliding portion of the radially outer portion by the insert molding of a resin material, in which fine recesses are formed at least on the portion of the surface of the radially outer portion that is in contact with the resin layer such that the sum of the apparent areas of the respective fine recesses on the surface of the radially outer portion accounts for 25 to 95% of the above portion of the surface of the radially outer portion. Further, the resin layer is configured such that the product of the linear expansion coefficient of the resin material forming the resin layer and the thickness of the resin layer is not more than 0.15.
Gate marks that develop while forming this high-precision slide bearing by injection molding may detrimentally influence the performance of the bearing. But disposing of such gate marks increases the production steps and thus reduces productivity.
In order to avoid this problem, the below-identified Patent document 2 proposes to form the resin layer on the sintered metal by insert molding in which molten resin is supplied through tunnel gates.
Such high-precision slide bearings are used as support bearings or carriage bearings for the photoconductor drum, developing unit or anchorage of copiers and printers.